1. Field of the Invention
The invention relates to supported modified Ziegler-Natta type transition-metal based catalysts, methods for making the same, methods of using the same and polymeric products obtained therefrom.
2. Description of the Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
The field of olefin catalysis has witnessed many remarkable discoveries during the last 50 years. In particular, two broad areas of invention having exceptional industrial importance stand out. First, in the 1950's the Ziegler-type catalysts were discovered and exploited in a variety of applications. Even today, these catalyst systems are used in many commercially important operations. Secondly, and more recently, the discovery of the "Metallocene"-type transition metal catalysts which are prepared with various cyclopentadiene and substituted cyclopentadiene derivatives have provided another important advance in polyolefin research and commercial products.
However, both of these important discoveries have certain limitations as known to those of ordinary skill in the art. Traditional Ziegler-Natta (hereafter referred to as Z-N) catalysts suffer from limited productivity, meaning the efficiency of conversion from monomer to polymer per unit of catalyst consumed is low. One method which has been attempted to enhance the productivity of traditional Z-N catalysts involves the pre-treatment or pre-activation of certain transition metal catalyst compositions using conventional aluminum alkyls.
In contrast, the metallocene-type catalysts possess extremely high rates of productivity. However, many commercial plants are not able to use such high levels of productivity and refitting such plants would be prohibitively expensive. Often, the amount of polymer produced is in excess of the down stream equipment's ability to process the product. Finally, large amounts of expensive alumoxane cocatalysts are required to initiate and sustain metallocene-based polymerizations. Consequently, these types of catalyst systems are sometimes modified by the addition of traditional Z-N catalysts (non-metallocene-type catalysts) to reduce the rates of productivity and thereby modify the properties of polymers produced to yield useful commercial products. These modifications are suggested to improve the molecular weight distributions and physical properties of polymers produced using these catalysts.
Thus, there appears to be an unmet, unfilled need in the field of olefin transition metal catalyst polymerization wherein the productivity or efficiency of the catalysts could be economically improved without compromising the useful characteristics of the resultant materials. More specifically, the improvements in productivity would mean that less catalyst is consumed thus resulting in significant economic savings in costs associated with producing a given quantity of polymer.
U.S. Pat. Nos. 4,701,432 and 5,183,867 to Welborn, Jr., et al., relate to supported olefin polymerization catalysts and processes of using same. These catalysts may contain at least one metallocene of a metal of Group IVB, VB, and VIB of the Periodic table, a non-metallocene transition metal-containing compound of a Group IVB, VB, or VIB metal and an alumoxane, the catalytic product being formed in the presence of the support. The catalyst is useful for the polymerization of olefins, especially ethylene and especially for the copolymerization of ethylene and other mono and diolefins. More specifically, the patents describe supported olefin catalyst systems wherein the catalyst components consist of a metallocene, a nonmetallocene transition metal component, an alumoxane and optionally, a cocatalyst system of an organic compound of a metal of Groups I-III of the Periodic Table, known to those skilled in the art as aluminum alkyls.
U.S. Pat. No. 5,183,867 to Welborn also relates to a two component transition metal complex for preparing polymers having multimodal molecular weight distributions (MWD).
U.S. Pat. No. 4,303,771 to Wagner et al. relates to a catalytic process for preparing ethylene polymers having a density between about 0.94 and 0.97 and a melt flow ratio of between about 22 and 32. The polymers are prepared in a low pressure reactor at a productivity of greater than or equal to 50,000 lbs of polymer per pound of Ti. The process uses a catalyst formed from selected organoaluminum compounds and a precursor composition being the reaction product of TiCl.sub.3, MgCl.sub.2, and THF as an electron donor (ED) compound in specific ratios. The aluminum alkyl is used as a "partially activating" agent before the catalyst is introduced into the reactor.
U.S. Pat. No. 4,302,566 to Karol et al. relates to the preparation of transition metal catalysts diluted with an inert carrier material and formed with selected organo aluminum compounds. Additionally, the Karol patent teaches specific activation sequences for the catalytic entities.
U.S. Pat. No. 4,124,532 to Giannini et al. describes the usefulness of incorporating various alkali and alkali earth metal complexes, e.g. MgCl.sub.2, into olefinic transition metal polymerization catalysts. These complexes are taught as having a positive effect on the activity of the polymerization of ethylene and alpha-olefins while being generally much less active than the corresponding transition metal halides.
It would be advantageous to provide a catalyst for olefin polymerizations having a useful range of productivity which is greater than that of a typical Z-N catalyst while less than that of many metallocene systems. It would be further useful to, at the same time, improve various physical properties of the polymers produced, e.g. molecular weight distributions and bulk density. Still another advantage would be improved flexibility in choosing the combinations of co-catalyst systems useful to preactivate and then activate the catalyst systems, while maintaining or improving the productivity and physical properties of the resultant polymers and copolymers.
None of the above-identified patents teach or suggest the beneficial effects of deliberate sequences of pre-activation and subsequent full activation of the catalysts using either alumoxanes alone or in conjunction with traditional aluminum alkyl type transition metal polymerization activators.